Among commercialized polyamide resins (nylons), poly(m-xylene adipamide) (MXD6) has been used in a variety of applications, such as film materials, injection molding materials, and the like due to its excellent rigidity, gas-barrier property, etc. MXD6 has an advantage over other nylons, because there are few problems associated with the protrusion of inorganic fillers, for example, glass fibers, from a surface of an article produced in an injection molding process due to slowed crystallization rate. Thus, MXD6 can provide molded products with a superior appearance due to reduced surface roughness.
PET/MXD6/PET, PA6/MXD6/PA6, and the like have been used as multilayer packaging films. Such multilayer films have been primarily prepared by a coextrusion process. However, MXD6 can be further polymerized by the heat generated during the extrusion of MXD6 to increase its molecular weight and melt viscosity, thereby making the extrusion process unstable. Furthermore, gel generation during extrusion can result in a poor appearance of the film, such as pin holes or fish eyes, etc. Gel generation can also reduce workability. Generally, it is known that a benzyl methyl structure included in MXD6 may form radicals under high temperature and oxygen contact conditions, thereby resulting in an increase in the molecular weight, gel forming, and the like.
Furthermore, MXD6 may have a reduced resistance to hot-humid external environments, since it has a reduced heat resistance compared with other high temperature resistant nylons.
Therefore, there is a need for a MXD6 based copolymerized polyamide resin that can reduce or prevent gel generation and can have improved heat resistance to expand the uses for MXD6 based polyamide resin.